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ESPRESSO spectrograph concept at the Preliminary Design Review.
ESPRESSO spectrograph optical design at the Preliminary Design Review.

ESPRESSO (Echelle SPectrograph for Rocky Exoplanet- and Stable Spectroscopic Observations)[1] is a new third-generation, high-resolution, fiber-fed and cross-dispersed echelle spectrograph (R = 140,000) for the visible wavelength range (350 nm – 720 nm), for the European Southern Observatory's Very Large Telescope (VLT). Its main feature is the spectroscopic stability and the radial velocity precision. With its very high spectroscopic precision, it will be able to detect Earth-like planets. For example, our Earth induces a radial-velocity variation of 9 cm/s on our Sun.[2] ESPRESSO will build on the foundations laid by the hugely successful High Accuracy Radial Velocity Planet Searcher (HARPS) instrument at the 3.6-metre telescope at ESO’s La Silla Observatory. ESPRESSO will benefit not only from the much larger combined light-collecting capacity of the four 8.2-metre VLT Unit Telescopes, but also from improvements in the stability and calibration accuracy that are now possible (for example, laser frequency comb technology).

The requirement is to reach 10 cm/s,[3] but the aimed goal is to obtain a precision level of a few cm/s. This would mean a large step forward over current radial-velocity spectrographs like ESO's HARPS. The highly successful HARPS instrument can attain a precision of 97 cm/s (3.5 km/h),[4] with an effective precision of the order of 30 cm/s,[5] making it one of only two instruments worldwide with such accuracy.[citation needed] The ESPRESSO would greatly exceed this capability making detection of earth-like planets from ground based instruments possible. Installation and commissioning of ESPRESSO at the VLT is foreseen in 2016.[2]

The instrument is capable of operating in 1-UT mode (using one of the telescopes) and in 4-UT mode. In 4-UT mode, in which all the four 8-m telescopes are connected incoherently to form a 16-m equivalent telescope the spectrograph will reach extremely faint objects.[2][6][7]


For example (for G2V type stars):

  • Rocky planets around stars as faint as V ~ 9 in (in 1-UT mode)
  • Neptune mass planets around stars as faint as V ~ 12 (in 4-UT mode )
  • Earth-like planets around stars as faint as V ~ 9 (CODEX on the E-ELT) (2025)[8]


Engineering rendering of the ESPRESSO instrument[9]
  • Schedule: First light on telescope: goal 2016
  • Preliminary Acceptance Europe, October 2015
  • Final Design Review, May 2013
  • Preliminary Design Review, November 2011
  • Kick off Meeting, January 2011
  • Phase A Study Review Meeting, March 2010

Scientific Objectives[edit]

The main scientific drivers for ESPRESSO are:

  • The measurement of high precision radial velocities of solar type stars for search for rocky planets.
  • The measurement of the variation of the physical constants (Search for possible variations of the constants of nature at different times and in different directions through the study of the light from very distant quasars).
  • The analysis of the chemical composition of stars in nearby galaxies.

These science cases require an efficient, high-resolution, extremely stable and accurate spectrograph.


ESPRESSO is being developed by a consortium consisting of ESO and seven further scientific institutes:

Comparison between ESPRESSO and CODEX[edit]

Telescope VLT (8m) E-ELT (39m)
Scope Rocky planets Earth-like
Sky aperture 1 arcsec 0.80 arcsec
R 150000 150000
λ coverage 350–730 nm 380–680 nm
λ precision m/s 1 m/s
RV stability < 10 cm/s < 2 cm/s
4-VLT mode
(D = 16 m)
with RV = 1 m/s


Radial velocity comparison tables[edit]

Planet Mass Distance
Radial velocity
Jupiter 1 28.4 m/s
Jupiter 5 12.7 m/s
Neptune 0.1 4.8 m/s
Neptune 1 1.5 m/s
Super-Earth (5 M⊕) 0.1 1.4 m/s
Alpha Centauri Bb (1.13 ± 0.09 M⊕) 0.04 0.51 m/s (1[10])
Super-Earth (5 M⊕) 1 0.45 m/s
Earth 1 0.09 m/s

Ref:[8] Notice 1: Most precise vradial measurements ever recorded. ESO's HARPS spectrograph was used.[10]

Planet Planet Type
Semimajor Axis
Orbital Period
Radial velocity
Detectable by:
51 Pegasi b Hot Jupiter 0.05 4.23 days 55.9[11] First-generation spectrograph
55 Cancri d Gas giant 5.77 14.29 years 45.2[12] First-generation spectrograph
Jupiter Gas giant 5.20 11.86 years 12.4[13] First-generation spectrograph
Gliese 581c Super-Earth 0.07 12.92 days 3.18[14] Second-generation spectrograph
Saturn Gas giant 9.58 29.46 years 2.75 Second-generation spectrograph
Alpha Centauri Bb Terrestrial planet 0.04 3.23 days 0.510[15] Second-generation spectrograph
Neptune Ice giant 30.10 164.79 years 0.281 Third-generation spectrograph
Earth Habitable planet 1.00 365.26 days 0.089 Third-generation spectrograph (likely)
Pluto Dwarf planet 39.26 246.04 years 0.00003 Not detectable

MK-type stars with planets in the habitable zone[edit]

Stellar mass
Planetary mass
0.10 1.0 8×10−4 M8 0.028 168 6
0.21 1.0 7.9×10−3 M5 0.089 65 21
0.47 1.0 6.3×10−2 M0 0.25 26 67
0.65 1.0 1.6×10−1 K5 0.40 18 115
0.78 2.0 4.0×10−1 K0 0.63 25 209

See also[edit]


  1. ^ "ESO - Espresso". Retrieved 2012-10-24. 
  2. ^ a b c "ESPRESSO - Searching for other Worlds". Centro de Astrofísica da Universidade do Porto. 2010-10-16. Retrieved 2010-10-16. 
  3. ^ Pepe, F.; Molaro, P.; Cristiani, S.; Rebolo, R.; Santos, N. C.; Dekker, H.; Mégevand, D.; Zerbi, F. M.; Cabral, A. et al. (January 2014). "ESPRESSO: The next European exoplanet hunter". Astronomische Nachrichten 335 (1): 8–20. arXiv:1401.5918. Bibcode:2014arXiv1401.5918P. doi:10.1002/asna.201312004. 
  4. ^ "32 planets discovered outside solar system -". CNN. 19 October 2009. Retrieved 4 May 2010. 
  5. ^ "ESPRESSO – Searching for other Worlds". Centro de Astrofísica da Universidade do Porto. 16 December 2009. Retrieved 2010-10-16. 
  6. ^ "ESPRESSO: the Echelle spectrograph for rocky exoplanets and stable spectroscopic observations". American Institute of Physics. July 2010. Retrieved 2013-03-12. 
  7. ^ "ESPRESSO: the Echelle spectrograph for rocky exoplanets and stable spectroscopic observations". ESO. July 2010. Retrieved 2013-03-12. 
  8. ^ a b c d "ESPRESSO and CODEX the next generation of RV planet hunters at ESO". Chinese Academy of Sciences. 2010-10-16. Retrieved 2010-10-16. 
  9. ^ "ESO Awards Contracts for Cameras for New Planet Finder". ESO Announcement. Retrieved 8 August 2013. 
  10. ^ a b "Planet Found in Nearest Star System to Earth". European Southern Observatory. 16 October 2012. Retrieved 17 October 2012. 
  11. ^ "51 Peg b". Exoplanets Data Explorer. 
  12. ^ "55 Cnc d". Exoplanets Data Explorer. 
  13. ^ Endl, Michael. "The Doppler Method, or Radial Velocity Detection of Planets". University of Texas at Austin. Retrieved 26 October 2012. 
  14. ^ "GJ 581 c". Exoplanets Data Explorer. 
  15. ^ "alpha Cen B b". Exoplanets Data Explorer. 
  16. ^ "An NIR laser frequency comb for high precision Doppler planet surveys". Chinese Academy of Sciences. 2010-10-16. Retrieved 2010-10-16. [dead link]